Pedal Powered Boats

[Guest625101138]

On the paddlewheel - This video shows relative performance of some different paddlewheels.
http://www.youtube.com/watch?v=-QjRM-cQpHw
It is mostly about size. If the size is right the feathering is a fringe benefit that is probably lost by the added weight.

On the submerged buoyancy - To get any benefit of standard displacement you have to be able to get the submerged hull very deep. At least 3 to 4 diameters to avoid wave drag. They are very difficult craft to make stable for human power. The submerged hull has a strong desire to get to the surface. There are some examples in the initial part of this video:
http://www.youtube.com/watch?v=kRuUtOmMGR0

Hydrofoils are better than submerged buoyancy if speed is desired. However the break even with well designed hydrofoils is around 220W as compared against the lowest drag displacement hull. Most people are not able to produce 220W for very long.

Rick W

[MLampi]

On a different topic, my Shimano cycling sandals finally gave up a couple of weeks ago. The bolts holding the Speedplay Frog cleats on one sandal rusted off. The rest of the sandal and the cleat are in almost perfect condition, but the cleat plate is heavily rusted and worthless.

Unfortunately, the cleat plate is also not replaceable in these sandals.

So, today I went and picked up a pair of Keen cycling sandals. These seem to be perhaps a little better designed in that not only do they have a toe cover but the cleat plate is trivially easy to replace.

They are a bit narrower and shorter than the Shimano sandals. They might work out a little better in the confines of the Cadence cockpit, too.

I'll find out this weekend at the Round Shaw Row, a 14 mile race in the San Juan Islands.

[Guest625101138]

Ian
The attached photo shows the curve in the cross beam from the load to your outrigger hull. Also shows the amount of roll on the main hull as a result.

Rick

[Dennis A]

Rick
On the proa to minimise drag, should the ama be just be toughing the water, the same as your outriggers or do you have to live with the drag of a further short displaemt hull.

Dennis

[Guest625101138]

Originally Posted by Dennis A

Rick
On the proa to minimise drag, should the ama be just be toughing the water, the same as your outriggers or do you have to live with the drag of a further short displaemt hull.

Dennis

Dennis
The set up Ian has is to get his pedal mounted gearbox over the side of the hull. This avoids the slot through the hull that he would need to make his boat easily beachable. He is positioned in line with the gearbox over the side of the main hull so his outrigger is load carrying.

With any single outrigger boat you need some weight carried by the outrigger to have stability. The modern outrigger canoes have height adjustment of the outrigger relative to the main hull. This alters the roll on the main hull that shifts the CoG inward or outward. It enables the boat to be set up for different pilots having different weights and ability to cope with instability.

I prefer twin outriggers because these can be completely unloaded and all the weight is carried on the main hull.

Ian's boat is quite stable because he has a lot of weight on the outrigger. There is extra drag over having all the weight carried on a single hull.

Rick

[I57]

The reason my boat is setup this way is to accomodate the involute gearbox. The gearbox has a 3.3 to 1 gear ratio and this allows for a very simple but effective setup. The shaft runs free at the side of the boat and only a small amount of the weight is carried by the outrigger (approx 15 kg). Outrigger is
3 metres long by 75mm wide and draft of 75mm, needs stronger bracing and height above main hull adjusted. Shaft is 8mm spring steel and the rudder springs up allowing the boat to sit flat on the beach. Thanks for the photo Rick and for the spring steel shaft.

Ian

[MLampi]

Originally Posted by MLampi

So, today I went and picked up a pair of Keen cycling sandals. These seem to be perhaps a little better designed in that not only do they have a toe cover but the cleat plate is trivially easy to replace.

They are a bit narrower and shorter than the Shimano sandals. They might work out a little better in the confines of the Cadence cockpit, too.

I'll find out this weekend at the Round Shaw Row, a 14 mile race in the San Juan Islands.

The Keen sandals are excellent. While wading through water, sand (wet and dry), weeds and rocks the sandals did a much better job than the Shimano sandals for protecting my feet and not scooping up detritus that my foot would subsequently be stepping on.

The narrower sandals enabled my feet to be able to release from the pedals at a much greater portion of the crank rotation than the other ones. There were no hot points and they remain quite comfortable throughout the race.

I think they are a winner. Now we'll see how they hold up over time.

Michael Lampi

[MLampi]

Rick, I'm interested in what you think about designing a "weedless" propeller that would exhibit reasonably high efficiency. My particular requirements are that the propeller not exceed 8.5 inches in diameter, spinning at roughly 520 rpm at a forward speed of 6.5 mph.

I'm picturing a narrow chord spiral scythe blade, so that incident weeds merely shoved aside rather than pulled in and wrapped around the shaft or prop blade.

Michael Lampi

[Guest625101138]

Originally Posted by MLampi

Rick, I'm interested in what you think about designing a "weedless" propeller that would exhibit reasonably high efficiency. My particular requirements are that the propeller not exceed 8.5 inches in diameter, spinning at roughly 520 rpm at a forward speed of 6.5 mph.

I'm picturing a narrow chord spiral scythe blade, so that incident weeds merely shoved aside rather than pulled in and wrapped around the shaft or prop blade.

Michael Lampi

Mike
I have assumed you get 6.5mph with 160W. This is about what I recall.

Your current 3-blade prop will achieve around 74% efficiency.

You can get 75% efficiency with 4-bladed prop.

If you were to go to a 1:2 gearbox and spin your prop at 1000rpm then you will get efficiency of 78%.

The effort that goes into making curved blades would be reduced if you can get away with 2 blades. There are some commercial 2-bladed props that are close to the right proportions.

My calculations are based on radial blades but the curve will not alter it a huge amount. Radially raked blades may be easier to make rather than curve them. You could have a small amount of curve on the leading edge.

I can give you a profile and twist using 30mm flatbar for the blades if you want to have a go. You will need to relate this to a raked blade.

To get the best efficiency at 520rpm you need to go up to 400mm diameter. With these conditions a practical prop would get 82% efficiency.

Rick

[Dennis A]

Weedless Props

I would love a weedless pedal system, unfortunately on a twisted chain drive, the prop is only one part of the weed catcher, the chain enclosure also does its part.
On my cat I use a puller system with the prop in the front as this seams to help the weed problem.
To make a prototype prop curved like a sickle, the blank curved blades could be cut from solid sheet rather than trying to bend flat bar which I think would require hot forging.

Dennis

[tinhorn]

Originally Posted by Rick Willoughby

If the size is right the feathering is a fringe benefit that is probably lost by the added weight.

Seems that the old-timers estimated feathering to increase paddlewheel efficiency by about 15%, but I can't find the sources for this.

As you undoubtedly recall, the 1813 Buchanan Parallel Paddle Wheel design provided ultimate articulation without the increased weight or complexity of feathering linkages or their attendant friction drag. Patent drawings of the less famous C.D. Town knockoff (1962) make the concept a little clearer.

I'm attaching references simply to refresh your memory.

[Guest625101138]

Originally Posted by tinhorn

Seems that the old-timers estimated feathering to increase paddlewheel efficiency by about 15%, but I can't find the sources for this.

......

The 15% improvement relates to a high slip wheel. If the wheel is big enough the slip is low anyhow.

The HPB racers using wheels have played with articulation but fixed blades, set for best compromise between angle of entry and exit, perform as well or better. Articulation is not worth the extra detail unless there is some constraint on the wheel size.

Rick W

[MLampi]

Originally Posted by Rick Willoughby

Mike
I have assumed you get 6.5mph with 160W. This is about what I recall.

Your current 3-blade prop will achieve around 74% efficiency.

You can get 75% efficiency with 4-bladed prop.

That is about what I calculate, too.

Originally Posted by Rick Willoughby

If you were to go to a 1:2 gearbox and spin your prop at 1000rpm then you will get efficiency of 78%.

Unfortunately, however, that also drops the service life of the gearbox or requires a much larger and heavier gearbox. I could use a 15 or 16 tooth small sprocket to get around 8:1. This would bring the speed of the prop up to 640 rpm at a cadence of 80.

Originally Posted by Rick Willoughby

The effort that goes into making curved blades would be reduced if you can get away with 2 blades. There are some commercial 2-bladed props that are close to the right proportions.

Are you referring to trolling motor blades?

Otherwise, with a spiral blade there might not be as much vibration as one sees with two straight blades. What commercial blades are thinking of?

Originally Posted by Rick Willoughby

My calculations are based on radial blades but the curve will not alter it a huge amount. Radially raked blades may be easier to make rather than curve them. You could have a small amount of curve on the leading edge.

To get the best efficiency at 520rpm you need to go up to 400mm diameter. With these conditions a practical prop would get 82% efficiency.

Rick

I don't think a small amount of curve would get the desired effect. Inertia and drag on the weeds will help, but the more of a curve that the blade has the slower the weed would have to move to get out of the way. They would be less likely to wrap around the blade.

Michael Lampi

[Guest625101138]

Mike
If you made a 3-bladed prop for 640rpm you could get efficiency up to 78%.

Any significant curve or skew (radial rake) on the blades will lower efficiency. I can only make estimates of how much it will impact. I think a skew of 30 degrees would be acceptable. It would be a little more if the blade tips were curved as well.

There are some commercial weedless props around but none have the pitch you require. You need a pitch around 13 to 14 inches. I have attached a picture of one of the small weedless props that have a nice shape but you can see the diameter is less and the pitch is way too small. If you could find something like 8X12 at the right price it would would be worth a try.

If you were going to make one then I suggest you start with the best prop you can fabricate and use this as a baseline. You then have the information to determine what the penalty is with skewed blades. If you just make the weedless blades then you really do not have anything to compare it with other than your current prop.

You would need some 1.25" by 1/8" stainless flatbar to make blades and a shaft coupling or heavy wall tube for a hub.

Rick W

[hollow hull]

Hi guys,
i am new on this forum,got here because i have an interest in pedalpowered
boats.
Has anyone considered or tried using a pedalpowered generator to power an electric outboard motor?
I have been toying with this thought, because it would not need a mechanical
transmission from pedal to prop